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Re: [libvirt] [PATCH] util: fix clear_emulator_capabilities=0



On 03/13/2013 06:09 PM, Eric Blake wrote:
> On 03/13/2013 01:37 PM, Laine Stump wrote:
>> My commit 7a2e845a865dc7fa82d2393ea2a770cfc8cf00b4 (and its
>> prerequisites) managed to effectively ignore the
>> clear_emulator_capabilities setting in qemu.conf (visible in the code
>> as the VIR_EXEC_CLEAR_CAPS flag when qemu is being exec'ed), with the
>> result that the capabilities are always cleared regardless of the
>> qemu.conf setting. This patch fixes it by passing the flag through to
>> virSetUIDGIDWithCaps(), which uses it to decide whether or not to
>> clear existing capabilities before adding in those that were
>> requested.
>>
>> Note that the existing capabilities are *always* cleared if the new
>> process is going to run as non-root, since the whole point of running
>> non-root is to have the capabilities removed (it's still possible to
>> add back individual capabilities as needed though).
>> ---
>> This will need to be backported to v1.0.3-maint.
> Yeah, now that Fedora 19 has branched and settled on 1.0.3 as its
> starting point, it looks like v1.0.3-maint will be getting lots of fixes :)
>
>> +        if (virSetUIDGIDWithCaps(cmd->uid, cmd->gid, cmd->capabilities,
>> +                                 (cmd->flags & VIR_EXEC_CLEAR_CAPS)) < 0) {
> While gnulib guarantees that we have <stdbool.h>, it also states that we
> cannot rely on C99 rules for slamming random integers into 1 when
> converting into a bool context (especially true for C89 compilers using
> gnulib's emulation, but apparently there are also buggy C99 compilers
> that miscompile things).  This should use '(cmd->flags &
> VIR_EXEC_CLEAR_CAPS) != 0' (or !! if you don't like != 0), just to be safe.
>
>> +    /* First drop all caps (unless the requested uid is "unchanged" or
>> +     * root and clearExistingCaps wasn't requested), then add back
>> +     * those in capBits + the extra ones we need to change uid/gid and
>> +     * change the capabilities bounding set.
>>       */
>>  
>> -    capng_clear(CAPNG_SELECT_BOTH);
>> +    if (clearExistingCaps || (uid != 1 && uid != 0))
> Did you mean uid != 0?

Well, actually I meant "uid != -1 && uid != 0" (and I had to look at it
5 times to see that the negative sign was missing).

I want to clear the existing caps if:

   A) clearExistingCaps is true (duh)

or

   B) The new uid will be different, and it will be something other than
root


>
> ACK with those problems addressed.
>


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